The Marine Corps said Thursday it staged regular live-fire drills on islands near the tensely guarded inter-Korean maritime border in the Yellow Sea. The exercise, involving K9 propelled howitzers and Chunmoo multiple launch rocket systems, took place on the islands of Baengnyeong and Yeonpyeong near the Northern Limit Line (NLL), the de facto maritime border. The drills, which are defensive in nature, are part of routine exercises held in waters south of the NLL, the Marine Corps said in a release. During the drills, troops reportedly fired some 330 rounds into surrounding waters, according to officials. It marked the second such drills this year, after the first session in February. The Northwest Islands Defense Command, the unit in charge of security on five islands in the Yellow Sea — Yeonpyeong, Baengnyeong, Daecheong, Socheong and U Island — conducts live-fire drills every three months.